Lagging sculpting with over 1 milion polygons on a High-End PC
I opened your file, and sculpting was definitely a little bit laggy, but nowhere near what you're describing (Having to wait 5 seconds before seeing the result of a sculpting change). However I managed to fix the problem by doing the following:

Hide the &quot;Teeth&quot;, &quot;Bones&quot;, and &quot;Eyes&quot; collections.
Important: Deactivate the Armature modifier from displaying in the viewport.


After I did this performance increased drastically for me.
Hope this helps!